The pea aphid, Acyrthosiphon pisum (Harris), is an important pest of alfalfa, Medicago sativa L., in Wisconsin because of its characteristic potential for exponential population growth (Hutchison and Hogg 1984, 1985) and the subsequent damage in both hay quality and quantity inflicted by high populations (Cuperus et al. 1982). In Wisconsin, as in most alfalfa-producing states, there is a vast complex of natural enemies (Hutchison and Hogg 1985) that influence pea aphid population dynamics, including the hymenopteran primary parasitoids from the Aphidiidae. These primary species, however, are also attacked by several secondary parasitoids from the families Megaspilidae, Pteromalidae, and Alloxystidae.

J.W.Johnson, R.D.Eikenbary, and D.Holbert. 1979. Parasites of the greenbug and other graminaceous aphids: identity based on larval meconium and features of the empty aphid mummy. Ann. ent. Soc. Am.72: 759–766.